What are the effects of cost sharing on health care utilization and health outcomes? While tremendous progress has been made on the answer to this question there remain some noticeable gaps in this literature. Most importantly more studies are necessary to understand how cost sharing affects the treatment of non- elderly adults and outcomes related to chronic diseases. This study exploits knowledge of how the Chilean government assigns individuals to health insurance plans in the public health insurance program in Chile (FONASA) to understand how cost-sharing affects health insurance utilization and health outcomes for adults in the Chilean health insurance system. FONASA assigns individuals from all across the adult age distribution into health insurance plans with varying levels of cost- sharing (0%, 10% and 20%) based on individual wage and household size. Using a regression discontinuity research design we propose to exploit this plan assignment procedure and aim to estimate causal estimates of the effects of cost sharing on health care utilization and health outcomes. This study will examine the effects on a variety of health utilization and health outcomes measures including physician, hospital, emergency room visits and asthma, hypertension, diabetes and depression detection.